How to solve java.lang.NoClassDefFoundError: org/springframework/beans/factory/SmartInitializingSingleton in Spring Boot [Solved]

Problem:
I was trying to run a HelloWorld program using Spring Boot when I got this error:

Exception in thread "main" java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration#propertySourcesPlaceholderConfigurer due to internal class not found. This can happen if you are @ComponentScanning a springframework package (e.g. if you put a @ComponentScan in the default package by mistake)
at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:52)
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:92)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForBeanMethod(ConfigurationClassBeanDefinitionReader.java:174)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForConfigurationClass(ConfigurationClassBeanDefinitionReader.java:136)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitions(ConfigurationClassBeanDefinitionReader.java:116)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:324)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:243)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:254)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:94)
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:609)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:464)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:117)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:689)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:321)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:969)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:958)
at boot.SpringBootDemo.main(SpringBootDemo.java:14)
Caused by: java.lang.NoClassDefFoundError: org/springframework/beans/factory/SmartInitializingSingleton
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
at
org.springframework.boot.autoconfigure.condition.OnBeanCondition.collectBeanNamesForType(OnBeanCondition.java:164)
at org.springframework.boot.autoconfigure.condition.OnBeanCondition.getBeanNamesForType(OnBeanCondition.java:153)
at org.springframework.boot.autoconfigure.condition.OnBeanCondition.getMatchingBeans(OnBeanCondition.java:121)
at org.springframework.boot.autoconfigure.condition.OnBeanCondition.getMatchOutcome(OnBeanCondition.java:95)
at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:46)
... 16 more
Caused by: java.lang.ClassNotFoundException: org.springframework.beans.factory.SmartInitializingSingleton
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
... 33 more




I had the correct starter dependency like spring-boot-starter-web and I was using @SpringBootApplication annotation on my Main class to run it inside an embedded container.

I had created a simple RESTful web service with a controller class returning "Hello Spring Boot" as shown below:

package boot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
public class SpringBootDemo {

  public static void main(String args[]) {
    SpringApplication.run(SpringBootDemo.class, args);
  }

}

@RestController
class HelloControler {

  @RequestMapping("/")
  public String hello() {
    return "Hello Spring Booot";
  }

}

And my pom.xml (Maven dependency file looked like below):

<project xmlns="http://maven.apache.org/POM/4.0.0" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
          http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>SpringMavenDemo</groupId>
    <artifactId>SpringMavenDemo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>MavenDemo</name>
    <build>
        <sourceDirectory>src</sourceDirectory>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>1.2.7.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.2.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>4.0.0.RELEASE</version>
        </dependency>

    </dependencies>
</project>

There are three errors in this stack trace:

1. The Caused by java.lang.ClassNotFoundException: org.springframework.beans.factory.SmartInitializingSingleton

2. The Caused by: java.lang.NoClassDefFoundError: org/springframework/beans/factory/SmartInitializingSingleton

3. Exception in thread "main" java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration#propertySourcesPlaceholderConfigurer due to internal class not found.

This can happen if you are @ComponentScanning a spring framework package (like if you put a @ComponentScan in the default package by mistake)

Solution:

The reason was following conflicting dependencies which I have already had in my project, precisely in the pom.xml.

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.2.3</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>4.0.0.RELEASE</version>
</dependency>

The main reason was an incompatible version of the Spring library in the classpath. Earlier I had used the spring-web 4.0.0 release but Spring Boot 1.2.7 web starters require a higher version of the library. The class which was in question i.e. SmartInitializingSingleton wasn't present in an earlier version of the library.

After I remove those maven dependencies, my project just ran fine. There was no error in the log file and I can see the Spring Boot printed in the log file. 

As shown in the following screenshot:

That's all about how to fix "java.lang.NoClassDefFoundError: org/springframework/beans/factory/SmartInitializingSingleton" error in Spring Boot. As with any other ClassNotFoundException or NoClassDefFoundError, this was also related to loading the wrong class from the classpath. 

Just be careful not to mix individual dependency with Spring boot starter dependency unless you are sure that the explicit dependency is complete, not present as part of starter dependency.

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